L15 - resp physio 3

Question 1

what is Va / Q

Answer 1

matching alveolar ventilation to total lung perfusion (Q)

Question 2

what does a higher Va / Q show

Answer 2

overventilated
under perfused

under perfused regions act like alveolar dead space

Question 3

what does lower Va / Q

Answer 3

under ventilated
over perfused

under ventilated regions behave like R to L shunts diluting the O2

Question 4

what is the normal Va /Q value

Answer 4

0.84

Question 5

what do higher / lower than normal Va/Q lead to?

Answer 5

reduced PO2

Question 6

what is anatomical R to L shunt

Answer 6

bronchiole veins draining into pulmonary vein

Question 7

hat are physiological R to L shunts

Answer 7

any other causes of the mixing of deoxy blood with oxy blood

Question 8

how can we compensate for mismatch in Va/Q caused by areas being poorly ventilated

Answer 8

hypoxic vasoconstriction

constrict arteries that go to poorly ventilated areas, so the blood flows through ventilated areas instead

Question 9

how does Va / Q mismatch occur in normal healthy lung

Answer 9

1. gravity causes Pip to become more negative at apex
   than base
2. causes Ptp to become more positive at apex
3. alveoli more expanded at apex (before inspiration)
4. alveoli at base are more able to expand - more
   ventilation at base
5. also causes more perfusion at base, apex arterioles may collapse at some points during cardiac cycle

Question 10

what contributes to resistance in airways

Answer 10

1. radius of tubes
2. no. of tubes in parallel
3. congestion
4. resistance decreases from trachea - bronchioles

Question 11

what causes bronchodilation (chemical/neural)

Answer 11

neuropeptides
CO2
adrenaline (B2)

Question 12

what causes bronchoconstriction (chemical/neural)

Answer 12

ACh (muscarinic Rs - PNS)

inflammatory cells

Question 13

what stimulates ACh to cause bronchoconstriction

Answer 13

1. irritant R’s

2. Stretch R’s

Question 14

what is lung compliance a measure of

Answer 14

measure of how easily lungs are expanded by given change in pressure
determines work needed to be done by respiratory muscles

Question 15

what physical factors affect respiratory resistance

Answer 15

1. increase in airway resistance eg asthma
2. inspiration decreases resistance
3. forced expiration (exercise) increases resistance

Question 16

what is surface tension

Answer 16

force in alveoli due to water cohesion

Question 17

function of surfactant

Answer 17

prevents alveolar collapse by reducing surface tension in smaller alveoli